An eyeglass prescription is an order written by an eyewear prescriber, such as an optometrist or ophthalmologist, that specifies the value of all parameters the prescriber has deemed necessary to construct and/or dispense corrective lenses appropriate for a patient. If an examination indicates that corrective lenses are appropriate, the prescriber generally provides the patient with an eyewear prescription at the conclusion of the exam.
The parameters specified on spectacle prescriptions vary, but typically include the power to which each lens should be made in order to correct blurred vision due to refractive errors, including myopia, hyperopia, astigmatism, and presbyopia. It is typically determined using a phoropter and asking the patient which of two lenses is better, or by computer automated refractor, or through the technique of retinoscopy. A dispensing optician will take a prescription written by an optometrist or ophthalmologist and order and/or assemble the frames and lenses to then be dispensed and sold to the patient.
In addition to the correction parameters certain physical parameters must be measured to ensure the proper fit of the corrective optic to the wearer. Two key parameters are pupillary distance and segment height or fitting height. Pupillary Distance (PD) is the distance between pupil centers, usually expressed in millimeters. It is sometimes known as the Interpupillary Distance (IPD). It is written as two values if the prescription is for bifocals or progressive lenses—these are the pupillary distances for the distance and near fixation (essentially, the upper and lower part of the lenses). They differ due to pupillary convergence when looking at near objects. Additionally, an eyeglasses prescription may include a monocular pupillary distance (“monocular PD”), especially in situations of non-symmetrical faces. These measurements indicate, in millimeters, the distances from the center of each pupil to the center of the nose where the center of the frame bridge rests. PD measurements are essential for all spectacle dispensings, monocular PDs being essential in progressive lenses and for those with high prescription. Segment Height (SH), also known as Seg Height, in a multifocal lens, such as a progressive or bifocal lens, also referred to as Fitting Height (FH) in single vision lens, is the vertical measurement in millimeters from the bottom of the lens in a frame, to the center of pupil for a single vision or a progressive lens, or to the bottom of lower eyelid for a lined bifocal. The determined segment height/fitting height is specific to each frame and wearer.
SH/FH and PD values are typically measured by a skilled professional using a pupilometer and/or by using a ruler. The need to have professional optical staff make these key measurements limits the ability of retailers to expand into the area of prescription optical frames, such as for example, for prescription sunglasses. Accordingly, a need exists for a simplified eyewear measuring system.